Vehicle roll control system

ABSTRACT

A vehicle roll control system, comprising a front torsion bar(22), attached to the front hydraulic actuator (34) and a rear torsion bar (24) attached to the rear hydraulic actuator (34′). A pressure control valve (99) is fluidly connected between a pressure source (80) and a reservoir (81). A directional valve (82) is fluidly connected between the pressure control valve (99) and the hydraulic actuators (34,34′). A pressure relief valve (83,84) fluidly connects the directional valve to the pressure source (80) or the reservoir (81) and is actuated to create pressure differential between first fluid chambers (58,58′) of the hydraulic actuators (34,34′)and/or to create pressure differential between second fluid chambers (60,60′) of the hydraulic actuators (34,34′).

TECHNICAL FIELD

The present invention relates to a roll control system for a motorvehicle.

BACKGROUND OF THE INVENTION

EP-A-1103395 discloses a vehicle roll control system in which a pair ofdirectional valves and a pressure control valve are used to control themovement of the piston of hydraulic actuators associated with the frontand rear axles of a motor vehicle. WO-A-03/093041 discloses a vehicleroll control system in which a pair of pressure control valves and adirectional valve are used to control the movement of the piston ofhydraulic actuators associated with the front and rear axles of a motorvehicle. In both cases, each hydraulic actuator has a first fluidchamber positioned on one side of the piston, and a second fluid chamberpositioned on the other side of the piston. The first fluid chambers ofthe front and rear hydraulic actuators receive hydraulic fluid atsubstantially the same pressure; and the second fluid chambers of thefront and rear hydraulic actuators receive hydraulic fluid atsubstantially the same pressure.

SUMMARY OF THE INVENTION

The aim of the present invention is to provide a roll control systemwhich is an improvement to the above mentioned arrangements.

A vehicle roll control system in accordance with the present inventionis characterised by the features specified in claim 1.

In the present invention, the control means for the hydraulic circuit iscapable of providing fluid pressure to the first fluid chamber of thefront hydraulic actuator which is different from the fluid pressureprovided to the first fluid chamber of the rear hydraulic actuator;and/or is capable of providing fluid pressure to the second fluidchamber of the front hydraulic actuator which is different from thefluid pressure provided to second fluid chamber of the rear hydraulicactuator.

The present invention provides a system which allows an aggressive rollcontrol strategy and balance strategy which leads to improvements inmotion, turning, and stability (braking in turn at high speed). Thepresent invention also provides continuous control between right turnand left turn.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a schematic presentation of a vehicle incorporating a vehicleroll control system in accordance with the present invention;

FIG. 2 is an enlarged view of the front and rear portions of the vehicleroll control system shown in FIG. 1;

FIG. 3 is a side view of the first arm of the vehicle roll controlsystem shown in FIG. 2;

FIG. 4 is a side view of the second arm, hydraulic actuator (shown incross-section) and lever arm of the vehicle roll control system shown inFIG. 2;

FIG. 5 is a schematic diagram of the hydraulic and electrical controlcircuit of the vehicle roll control system shown in FIG. 1 when thedirectional valve and pressure relief valves are de-actuated or in theirfail-safe mode;

FIG. 6 is a schematic diagram of a first alternative hydraulic andelectrical control circuit of the vehicle roll control system shown inFIG. 1 when the directional valve and the pressure relief valves arede-actuated or in their fail-safe mode;

FIG. 7 is a schematic diagram of a second alternative hydraulic andelectrical control circuit of the vehicle roll control system shown inFIG. 1 when the directional valve and the pressure relief valves arede-actuated or in their fail-safe mode;

FIG. 7A is a schematic diagram of a third alternative hydraulic andelectrical control circuit of the vehicle roll control system shown inFIG. 1 when the directional valve and the pressure relief valves arede-actuated or in their fail-safe mode;

FIG. 8 is a schematic diagram of a fourth alternative hydraulic andelectrical control circuit of the vehicle roll control system shown inFIG. 1 when the directional valve and the pressure relief valves arede-actuated or in their fail-safe mode;

FIG. 8A is a schematic diagram of a fifth alternative hydraulic andelectrical control circuit of the vehicle roll control system shown inFIG. 1 when the directional valve and the pressure relief valves arede-actuated or in their fail-safe mode;

FIG. 9 is a schematic diagram of a sixth alternative hydraulic andelectrical control circuit of the vehicle roll control system shown inFIG. 1 when the directional valve and the pressure relief valves arede-actuated or in their fail-safe mode;

FIG. 9A is a schematic diagram of a seventh alternative hydraulic andelectrical control circuit of the vehicle roll control system shown inFIG. 1 when the directional valve and the pressure relief valves arede-actuated or in their fail-safe mode;

FIG. 10 is a schematic diagram of an eighth alternative hydraulic andelectrical control circuit of the vehicle roll control system shown inFIG. 1 when the directional valves and the pressure relief valve arede-actuated or in their fail safe mode;

FIG. 11 is a schematic diagram of a ninth alternative hydraulic andelectrical control circuit of the vehicle roll control system shown inFIG. 1 when the directional valves and the pressure relief valve arede-actuated or in their fail safe mode;

FIG. 12 is a view of a portion of a vehicle roll control system inaccordance with a second embodiment of the present invention;

FIG. 13 is a view of a portion of a vehicle roll control system inaccordance with a third embodiment of the present invention;

FIG. 14 is a cross-section view of the hydraulic actuator of the vehicleroll control system of FIG. 13;

FIG. 15 is a cross-sectional view of an alternative embodiment ofhydraulic actuator for the vehicle roll control system of FIG. 13; and

FIG. 16 is a cross-sectional view of a further alternative embodiment ofhydraulic actuator for the vehicle roll control system of FIG. 13.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, a vehicle 10 is shown schematically and comprises apair of front wheels 12 each rotatably mounted on an axle 14, a pair ofrear wheels 16 each rotatably mounted on an axle 18, and a shockabsorbing system 20 associated with each wheel. A portion 22 of avehicle roll control system in accordance with the present invention isassociated with the front wheels 12, and a portion 24 of the vehicleroll control system in accordance with the present invention isassociated with the rear wheels 16. The portions 22, 24 aresubstantially the same but with modifications made solely to allowfitting to the vehicle 10.

Referring in more detail to FIGS. 2 to 4, the portion 22 of the vehicleroll control system for the front of the vehicle comprises a torsion bar26, a first arm 28, a second arm 30, a lever arm 32, and a hydraulicactuator 34. The torsion bar 26 is mounted on the vehicle by a pair ofresilient mounts 36 in conventional manner to extend longitudinallybetween the wheels 12. The first arm 28 (FIG. 3) is fixed at one end 38by a splined connection 40 to the torsion bar 26. The other end 42 ofthe first arm 28 is connected to the axle 14 of one of the front wheels12 by a tie rod 43. The second arm 30 (FIG. 4) is rotatably mounted atone end 44 on the torsion bar 26 by way of a bearing 46. The other end48 of the second arm 30 is connected to the axle 14 of the other frontwheel 12 by a tie rod 49. The first and second arms 28,30 extendsubstantially parallel to one another when the vehicle is stationary,and substantially perpendicular to the torsion bar 26.

The lever arm 32 (FIG. 4) is fixed at one end 50 to the torsion bar 26by a splined connection 52 substantially adjacent the one end 44 of thesecond arm 30 and the bearing 46. The lever arm 32 extends substantiallyperpendicular to the torsion bar 26 to a free end 54. The fronthydraulic actuator 34 (FIG. 4) extends between, and is connected to, thefree end 54 of the lever arm 32 and the other end 48 of the second arm30. The front hydraulic actuator 34 comprises a housing 56 which definesfirst and second fluid chambers 58,60 separated by a piston 62 whichmakes a sealing sliding fit with the housing. As shown in FIG. 4, thehousing 56 is connected to the other end 48 of the second arm 30, andthe piston 62 is connected to the free end 54 of the lever arm 32 by apiston rod 64 which extends through the second fluid chamber 60. It willbe appreciated that these connections may be reversed. The fluidchambers 58,60 contain hydraulic fluid and are fluidly connected tofluid lines 66, 68 respectively. The portion 24 of the vehicle rollcontrol for the rear of the vehicle is substantially the same, but withthe components (which are primed) having a different layout. The rearhydraulic actuator 34′ is substantially the same as the front hydraulicactuator 34.

The hydraulic and electrical control circuit of the vehicle roll controlsystem of FIGS. 1 to 4 is shown in FIG. 5. The hydraulic circuitincludes a fluid pump 80, a fluid reservoir 81, a directional valve 82,a first pressure relief valve 83, a second pressure relief valve 84, anda pressure control valve 99. The directional valve 82 has eight ports85-92. The first pressure relief valve 83 has three ports 93-95. Thesecond pressure relief valve 84 has three ports 96-98. The pressurecontrol valve 99 is fluidly connected between the pump 80 and thereservoir 81. Fluid filters may be positioned after the pump 80 and/orbefore the reservoir 81.

The directional valve 82 has a first port 85 fluidly connected to thefluid pump 80; a second port 86 fluidly connected to the first port 93of the first pressure relief valve 83; a third port 87 fluidly connectedto the fluid pump 80; a fourth port 88 fluidly connected to the firstport 96 of the second pressure relief valve 84; a fifth port 89 fluidlyconnected to the first chamber 58′ of the rear actuator 34′ by way offluid line 66′; a sixth port 90 fluidly connected to the second chamber60′ of the rear actuator 34′ by way of fluid line 68′; a seventh port 91fluidly connected to the first chamber 58 of the front actuator 34 byway of fluid line 66; and an eighth port 92 fluidly connected to thesecond chamber 60 of the front actuator 34 by way of fluid line 68. Thedirectional valve 82 is solenoid actuated, and has a de-actuated state(shown in FIG. 5) in which the first and second ports 85,86 are fluidlyconnected; the third and fourth ports 87,88 are fluidly connected; thefifth and seventh ports 89,91 are fluidly connected; and the sixth andeighth ports 90,92 are fluidly connected. In the actuated state of thedirectional valve 82, the first and eighth ports 85,92 are fluidlyconnected; the second and seventh ports 86,91 are fluidly connected; thethird and sixth ports 87,90 are fluidly connected; and the fourth andfifth ports 88,89 are fluid connected. In an alternative arrangement,the directional valve 82 may be hydraulically actuated by first andsecond pilot (on/off) valves (not shown).

The second port 94 of the first pressure relief valve 83 is fluidlyconnected to the pump 80. The third port 95 of the first pressure reliefvalve 83 is fluidly connected to the reservoir 81. In the de-actuatedstate of the first pressure relief valve 83 (shown in FIG. 5), the firstport 93 is fluidly connected to the third port 95, and the second port94 is fluidly isolated. In the actuated state of the first pressurerelief valve 83, the first port 93 is fluidly connected to the secondport 94, and the third port 95 is fluidly isolated.

The second port 97 of the second pressure relief valve 84 is fluidlyconnected to the pump 80. The third port 98 of the second pressurerelief valve 84 is fluidly connected to the reservoir 81. In thede-actuated state of the second pressure relief valve 84 (shown in FIG.5), the first port 96 is fluidly connected to the third port 98, and thesecond port 97 is fluidly isolated. In the actuated state of the secondpressure relief valve 84, the first port 96 is fluidly connected to thesecond port 97, and the third port 98 is fluidly isolated.

The first and second pressure relief valves 83,84 are preferablysolenoid actuated as shown in FIG. 5. Alternatively, the pressure reliefvalves 83,84 may be hydraulically actuated by first and second pilot(on/off) valves (not shown).

The pump 80 may be driven by the vehicle engine and hence continuouslyactuated. Alternatively, the pump 80 may be driven by an electric motoror any other suitable means, either continuously, or variably. Thepressure control valve 99 is actuated to adjust the fluid pressure inthe hydraulic system between a predetermined minimum pressure and apredetermined maximum pressure. The pressure control valve 99 is alsoactuated to adjust the pressure differential between the first andsecond chambers 58, 58′,60, 60′ of the hydraulic actuators 34,34′respectively (when the directional valve 82 and pressure relief valves83,84 are also actuated as required).

The electrical control circuit includes an electronic and/orcomputerised control module 70. The control module 70 operates the fluidpump 80, the directional valve 82, the pressure control valve 99, andthe pressure relief valves 83,84, when required. The control module 70actuates the valves 82-84,99 dependent on predetermined vehicleconditions which are determined by signals from one or more sensors,such as a first pressure sensor 76 (which detects the fluid pressureassociated with the first chamber 58 of the front hydraulic actuator34), a second pressure sensor 77 (which detects the fluid pressureassociated with the first chamber 58′ of the rear hydraulic actuator34′), a third pressure sensor 75 (which detects the fluid pressureassociated with the second chambers 60,60′ of the actuators 34,34′), alateral g sensor 74 (which monitors the sideways acceleration of thevehicle), a steering sensor 72 (which monitors the steering angle of thefront wheels 12), a vehicle speed sensor 78, and/or any other relevantparameter.

If the control module 70 detects that roll control is required (due, forexample, to cornering of the motor vehicle 10), the control moduledetermines if the module has to generate a force F, F′ which acts on thepiston rods 64,64′ respectively to extend the front and/or rearactuators 34,34′, or to compress the front and/or rear actuators, in anaxial direction. In the present invention, the force F on the frontactuator 34 may be different from the force F′ on the rear actuator 34′dependent on the actuation of the pressure relief valves 83,84; and thevalue of the pressure differential is set by the pressure control valve99.

In this embodiment, the roll control system can be operated in fourdifferent modes when the directional valve 82 is actuated and thepressure control valve 99 is actuated. In a first mode, when the firstpressure relief valve 83 is actuated and the second pressure reliefvalve 84 is de-actuated, the second fluid chambers 60, 60′ of the frontand rear hydraulic actuators 34, 34′ are at substantially the samepressure, the first fluid chamber 58 of the front hydraulic actuator isat a pressure which is substantially equal to or less than the pressurein the second chambers dependent on the pressure relief valve 83, andthe first fluid chamber 58′ of the rear hydraulic actuator is at adifferent pressure. In a second mode, when the first pressure reliefvalve 83 is de-actuated and the second pressure relief valve 84 isactuated, the second fluid chambers 60, 60′ of the front and rearhydraulic actuators 34, 34′ are at substantially the same pressure, thefirst fluid chamber 58′ of the rear hydraulic actuator is a pressurewhich is substantially equal to or less than the pressure in the secondchambers dependent on the pressure relief valve 84, and the first fluidchamber 58 of the front hydraulic actuator is at a different pressure.In a third mode, when the pressure relief valves 83, 84 are de-actuated,the first fluid chambers 58, 58′ of the hydraulic actuators 34, 34′ areat substantially the same pressure, and the second fluid chambers 60,60′ of the hydraulic actuators are at substantially the same pressurebut at a different pressure to the first fluid chambers. In a fourthmode, when the pressure relief valves 83, 84 are actuated, the secondfluid chambers 60,60′ of the front and rear hydraulic actuators 34, 34′are at substantially the same pressure, the first fluid chamber 58 ofthe front hydraulic actuator is at a pressure which is substantiallyequal to or less than the pressure in the second chambers dependent onthe pressure relief valve 83, and the first fluid chamber 58′ of therear hydraulic actuator is at a pressure which is substantially equal toor less than the pressure in the second chambers dependent on thepressure relief valve 84. Also, in this fourth mode, the pressures inthe first chambers 58, 58′ may be different from one another dependenton the pressure relief valves 83, 84. In all of the above modes, thevalue of any pressure differential is control by the pressure controlvalve 99 and the pressure relief valves 83, 84. This arrangementprovides improvement management of the compression or expansion of thehydraulic actuators, and hence provides improved roll control of thevehicle.

FIG. 6 illustrates a first alternative of the hydraulic and electricalcontrol circuit of the vehicle roll control system shown in FIGS. 1 to4. FIG. 6 is a modification of the hydraulic circuit shown in FIG. 5, inwhich changes have been made to the directional valve 82. In thisalternative, in the de-actuated state of the directional valve 82, thefifth, sixth, seventh and eighth ports 89-92 are fluidly isolated fromone another and from the other ports 85-88. The operation of this firstalternative is substantially the same as the operation of thearrangement shown in FIG. 5.

FIG. 7 illustrates a second alternative of the hydraulic and electricalcontrol circuit of the vehicle roll control system shown in FIGS. 1 to4. FIG. 7 is a modification of the hydraulic circuit shown in FIG. 5, inwhich changes have been made to the directional valve 482. In thisalternative, the directional valve 482 comprises six ports, a first port485, a second port 486, a third port 487, a fourth port 488, a fifthport 489 and a sixth port 490. The first port 485 is fluidly connectedto the pump 80. The second port 486 is fluidly connected to the firstport 93 of the first pressure relief valve 83. The third port 487 isfluidly connected to the first port 96 of the second pressure reliefvalve 84. The fourth port 488 is fluidly connected to the first fluidchamber 58′ of the rear actuator 34′. The fifth port 489 is fluidlyconnected to the first fluid chamber 58 of the front actuator 34. Thesixth port 490 is fluidly connected to the second fluid chambers 60, 60′of the front and rear actuators 34, 34′. In the de-actuated state of thedirectional valve 482, the first, second, third and sixth ports 485-487,490 are fluidly isolated from one another and from the other ports 488,489 (which are fluidly connected). The operation of this secondalternative is substantially the same as the operation of thearrangement shown in FIG. 5.

FIG. 7A illustrates a third alternative of the hydraulic and electricalcontrol circuit of the vehicle roll control system shown in FIGS. 1 to4. FIG. 7A is a modification of the hydraulic and electrical circuitshown in FIG. 7, in which changes have been made to the operation of thedirectional valve 482′. In this alternative, the directional valve 482′is hydraulically actuated (rather than solenoid actuated) by first andsecond pilot (on/off) valves 491, 492. The pilot valve 491, 492 arefluidly connected in series between the pump 80 and the reservoir 81.The actuator 493 for the directional valve 482′ is fluidly connected tothe flow path between the pilot valves 491, 492. The operation of thepilot valves 491, 492 is controlled by the control module 70. Other thanthe actuation of the directional valve 482′ by the pilot valves 491,492, the operation of this third alternative is substantially the sameas the operation of the arrangement shown in FIG. 5.

FIG. 8 illustrates a fourth alternative of the hydraulic and electricalcontrol circuit of the vehicle roll control system shown in FIGS. 1 to4. FIG. 8 is a modification of the hydraulic circuit shown in FIG. 7, inwhich changes have been made to the directional valve 482. In thisalternative, in the de-actuated state of the directional valve 482, thefirst, second and third ports 485-487 are fluidly connected to oneanother. The operation of this fourth alternative is substantially thesame as the operation of the arrangement shown in FIG. 5.

FIG. 8A illustrates a fifth alternative of the hydraulic and electricalcontrol circuit of the vehicle roll control system shown in FIGS. 1 to4. FIG. 8A is a modification of the hydraulic and electrical circuitshown in FIG. 8, in which changes have been made to the operation of thedirectional valve 482′. In this alternative, the directional valve 482′is hydraulically actuated (rather than solenoid actuated) by first andsecond pilot (on/off) valves 491, 492. The pilot valve 491, 492 arefluidly connected in series between the pump 80 and the reservoir 81.The actuator 493 for the directional valve 482′ is fluidly connected tothe flow path between the pilot valves 491, 492. The operation of thepilot valves 491, 492 is controlled by the control module 70. Other thanthe actuation of the directional valve 482′ by the pilot valves 491,492, the operation of this fifth alternative is substantially the sameas the operation of the arrangement shown in FIG. 5.

FIG. 9 illustrates a sixth alternative of the hydraulic and electricalcontrol circuit of the vehicle roll control system shown in FIGS. 1 to4. FIG. 9 is a modification of the hydraulic circuit shown in FIG. 7, inwhich changes have been made to the directional valve 482. In thisalternative, in the de-actuated state of the directional valve 482, thesecond and third ports 485-487 are fluidly connected to one another,whilst the first and sixth ports 485, 490 are fluidly isolated. Theoperation of this sixth alternative is substantially the same as theoperation of the arrangement shown in FIG. 5.

FIG. 9A illustrates a seventh alternative of the hydraulic andelectrical control circuit of the vehicle roll control system shown inFIGS. 1 to 4. FIG. 9A is a modification of the hydraulic and electricalcircuit shown in FIG. 9, in which changes have been made to theoperation of the directional valve 482′. In this alternative, thedirectional valve 482′ is hydraulically actuated (rather than solenoidactuated) by first and second pilot (on/off) valves 491, 492. The pilotvalve 491, 492 are fluidly connected in series between the pump 80 andthe reservoir 81. The actuator 493 for the directional valve 482′ isfluidly connected to the flow path between the pilot valves 491, 492.The operation of the pilot valves 491, 492 is controlled by the controlmodule 70. Other than the actuation of the directional valve 482′ by thepilot valves 491, 492, the operation of this seventh alternative issubstantially the same as the operation of the arrangement shown in FIG.5.

The above-described embodiments all operate in substantially the sameway, but provide different hydraulic circuit arrangements for theirrespective fail-safe modes, as illustrated in the drawings. Also, theselection is dependent on the type of hydraulic actuator that is used.

FIG. 10 illustrates an eighth alternative of the hydraulic andelectrical control circuit of the vehicle roll control system shown inFIGS. 1 to 4. FIG. 10 is a modification of the hydraulic circuit shownin FIG. 5, in which the second pressure relief valve has been removed,and a second directional valve 184 is positioned between the firstdirectional valve 82 and the pump 80 and reservoir 81.

The second directional valve 184 has a first port 185 fluidly connectedto the fluid pump 80; a second port 186 fluidly connected to thereservoir 81; a third port 187 fluidly connected to the first port 93 ofthe pressure relief valve 83; a fourth port 188 fluidly connected to thereservoir 81; a fifth port 189 fluidly connected to the fourth port 88of the first directional valve 82; a sixth port 190 fluidly connected tothe third port 87 of the first directional valve 82; a seventh port 191fluidly connected to the second port 86 of the first directional valve82; and an eighth port 192 fluidly connected to the first port 85 of thefirst directional valve 82. The second directional valve 184 is solenoidactuated, and has a de-actuated state (shown in FIG. 10) in which thefirst and eighth ports 185,192 are fluidly connected; the second andseventh ports 186,191 are fluidly connected; the third and sixth ports187,190 are fluidly connected; and the fourth and fifth ports 188,189are fluidly connected. In the actuated state of the second directionalvalve 184, the first, seventh and eighth ports 185,191,192 are fluidlyconnected; the third, fifth and sixth ports 187,189,190 are fluidlyconnected; and the second and fourth ports 186,188 are fluidly isolated.

Also, in this eighth alternative, there are only two pressure sensors76′,77′. The first pressure sensor 76′ detects the fluid pressure.associated with the front hydraulic actuator 34, and a second pressuresensor 77′ detects the fluid pressure associated with the rear hydraulicactuator 34′.

In this embodiment, the roll control system can be operated in fourdifferent modes when the directional valve 82 is actuated. In a firstmode, when the first pressure relief valve 83 is de-actuated and thesecond directional valve 184 is de-actuated, the first and second fluidchambers 58′, 60′ of the rear hydraulic actuator 34′ and the first fluidchamber 58 of the front hydraulic actuator 34 are at substantially thesame pressure, and the second fluid chamber 60 of the front hydraulicactuator is at a different pressure. In a second mode, when the firstpressure relief valve 83 is actuated and the second differential valve184 is de-actuated, the first fluid chambers 58, 58′ of the front andrear hydraulic actuators 34, 34′ are at substantially the same pressure,the second fluid chamber 60 of the front hydraulic actuator is at adifferent pressure to the first fluid chambers, and the second fluidchamber 60′ of the rear hydraulic actuator is a pressure which issubstantially equal to or less than the pressure in the second chamberof the front hydraulic actuator dependent on the pressure relief valve83. In a third mode, when the pressure relief valve 83 is de-actuatedand the second direction valve 184 is actuated, the first and secondfluid chambers 58, 60 of the front hydraulic actuator 34 are atsubstantially the same pressure, and the first and second fluid chambers58′, 60′ of the rear hydraulic actuator 34′ are at substantially thesame pressure but at a different pressure to the fluid chambers of thefront actuator. In a fourth mode, when the pressure relief valve 83 andthe second directional valve 184 are actuated, the first and secondfluid chambers 58, 60 of the front hydraulic actuator 34 are atsubstantially the same pressure, and the first and second fluid chambers58′,60′ of the rear hydraulic actuator 34′ are at substantially the samepressure which is substantially the same as or less than the pressure inthe fluid chambers of the front actuator dependent on the pressurerelief valve 83. In the above modes, the value of any pressuredifferential is control by the pressure control valve 99 and thepressure relief valve 83. This arrangement provides improvementmanagement of the compression or expansion of the hydraulic actuators,and hence provides improved roll control of the vehicle.

Although the directional valves 82, 184 are shown as solenoid actuated,these valves may, as an alternative, be hydraulically actuated by pilot(on/off) valves.

FIG. 11 illustrates a ninth alternative of the hydraulic and electricalcontrol circuit of the vehicle roll control system shown in FIGS. 1 to4. FIG. 11 is a modification of the hydraulic circuit shown in FIG. 11,in which changes have been made to the first directional valve 82. Inthis alternative, in the de-actuated state of the first directionalvalve 82, the fifth, sixth, seventh and eighth ports 89-92 are fluidlyisolated from one another and from the other ports 85-88. The operationof this ninth alternative is substantially the same as the operation ofthe arrangement shown in FIG. 10.

The above-described embodiments of FIGS. 10 and 11 both operate insubstantially the same way, but provide different hydraulic circuitarrangements for their respective fail-safe modes, as illustrated in thedrawings. Also, the selection is dependent on the type of hydraulicactuator that is used.

In the present invention, in all of the above embodiments, the valves ofthe hydraulic circuit are actuable to provide fluid pressure to thefirst fluid chamber of the front hydraulic actuator which is differentfrom the fluid pressure provided to the first fluid chamber of the rearhydraulic actuator; and/or actuable to provide fluid pressure to thesecond fluid chamber of the front hydraulic actuator which is differentfrom the fluid pressure provided to second fluid chamber of the rearhydraulic actuator.

The present invention is also applicable for use with a vehicle rollcontrol system, the front portion 122 of which is as shown in FIG. 12and the rear portion of which is substantially identical to the frontportion. In this embodiment in accordance with the present invention,the front portion 122 comprises a torsion bar 126, a first arm 128, anda hydraulic actuator 134. The first arm 128 is fixed at one end 138 toone end 140 of the torsion bar 126. The other end 142 of the first arm128 is connected to one of the shock absorbers 120. The hydraulicactuator 134 has a piston rod 164 which is fixed to the other end 187 ofthe torsion bar 126. The housing 156 of the actuator 134 is connected tothe other shock absorber 120. The hydraulic actuator 134 issubstantially the same as the actuator 34 described above with referenceto FIGS. 1 to 5, and has a fluid line 166 connected to a first fluidchamber inside the housing, and another fluid line 168 connected to asecond fluid chamber inside the housing. The first and second fluidchambers inside the housing 156 are separated by a piston secured to thepiston rod 164. The fluid lines 166,168 for each hydraulic actuator areconnected to a hydraulic circuit as shown in FIG. 5, which is controlledby a control circuit as shown in FIG. 5, or any one of the arrangementsshown in FIGS. 6 to 11. The roll control system is operated insubstantially the same manner as that described above with reference toFIGS. 1 to 5, or any one of FIGS. 6 to 11.

The present invention is also applicable for use with a vehicle rollcontrol system as shown in FIG. 13. In this third embodiment inaccordance with the present invention, the front portion 222 of thesystem comprises a torsion bar 226, a first arm 228, a second arm 228′,and a hydraulic actuator 234. The rear portion of the system issubstantially identical. The first arm 228 is fixed at one end 238 toone end 240 of the torsion bar 226. The other end 242 of the first arm228 is connected to one of the shock absorbers 220. The second arm 228′is fixed at one end 238′ to the other end 287 of the torsion bar 226.The other end 242′ of the second arm 228′ is connected to the othershock absorber 220′. The torsion bar 226 is split into first and secondparts 290,292, respectively. The first and second parts 290,292 of thetorsion bar 226 have portions 294,296, respectively, which are axiallyaligned. The axially aligned portions 294,296 are connected by ahydraulic actuator 234.

The hydraulic actuator 234, as shown in FIG. 14, comprises a cylindricalhousing 256 which is connected at one end 239 to the portion 294 of thefirst part 290 of the torsion bar 226. The actuator 234 furthercomprises a rod 241 positioned inside the housing 256, extending out ofthe other end 243 of the housing, and connectable to the portion 296 ofthe second part 292 of the torsion bar 226. The rod 241 has an externalscrew thread 249 adjacent the housing 256. Balls 251 are rotatablypositioned in hemispherical indentations 253 in the inner surface 255 ofthe housing 256 adjacent the screw thread 249. The balls 251 extend intothe screw thread 249. The rod 241 is slidably and rotatably mounted inthe housing 256 at the other end 243 by way of a bearing 259 positionedin the other end 243. This arrangement allows the rod 241 to rotateabout its longitudinal axis relative to the housing 256, and to slide inan axial direction A relative to the housing. A piston chamber 261 isdefined inside the housing 256. The rod 241 sealing extends into thepiston chamber 261 to define a piston rod 264, and a piston 262 issecured to the end of the piston rod inside the piston chamber. Thepiston 262 makes a sealing sliding fit with the housing 256 and dividesthe chamber 261 into a first fluid chamber 258 and a second fluidchamber 260. The first fluid chamber 258 is fluidly connected to fluidline 266, and the second fluid chamber 260 is fluidly connected to fluidline 268.

The fluid lines 266,268 are connected to a hydraulic circuit as shown inFIG. 5, which is controlled by a control circuit as shown in FIG. 5, orany one of the arrangements shown in FIGS. 6 to 11. The roll controlsystem 222 is operated in substantially the same manner as thatdescribed above with reference to FIGS. 1 to 5, or any one of FIGS. 6 to11

An alternative arrangement for the hydraulic actuator of FIG. 14 isshown in FIG. 15. In this alternative embodiment, the actuator 334comprises a cylindrical housing 356 which is connected at one end 339 tothe portion 294 of the first part 290 of the torsion bar 226. Theactuator 334 further comprises a rod 341 positioned inside the housing356, extending out of the other end 343 of the housing, and connectableto the portion 296 of the second part 292 of the torsion bar 226. Therod 341 has an external screw thread 349 adjacent the housing 356. Balls351 are rotatably positioned in hemispherical indentations 353 in theinner surface 355 of the housing 356 adjacent the screw thread 349. Theballs 351 extend into the screw thread 349. The rod 341 is sidably androtatably mounted in the housing 356 at the other end 343 of the housingby way of a bearing 359 positioned in the other end. The rod 341 makes asliding guiding fit with the inner surface 355 of the housing 356 at itsend 341′ remote from the second part 292 of the torsion bar 226. Thisarrangement allows the rod 341 to rotate about its longitudinal axisrelative to the housing 356, and to slide in an axial direction Arelative to the housing. First and second fluid chambers 358,360 aredefined inside the housing 356. The rod 341 makes a sealing fit with theinner surface 355 of the housing 356 by way of seal 371 to define apiston 362. The first fluid chamber 358 is positioned on one side of thepiston 362, and the second fluid chamber 360 is positioned on the otherside of the piston. A seal 369 is positioned adjacent the bearing 359. Aportion 364 of the rod 341 defines a piston rod which extends throughthe second fluid chamber 360. The first fluid chamber 358 is fluidlyconnected to fluid line 366, and the second fluid chamber 360 is fluidlyconnected to fluid line 368. The fluid lines 366,368 are fluidlyconnected with one of the hydraulic circuits shown in FIGS. 5 to 11 toactuate the actuator 334.

A further alternative arrangement of hydraulic actuator 334′ is shown inFIG. 16. In this further alternative embodiment, the actuator 334′ issubstantially the same as the actuator 334 shown in FIG. 15, but withoutthe sliding guiding fit of the free end 341′ of the rod 341 with thehousing 356.

In a preferred arrangement, the cross-sectional area of the first fluidchamber of each hydraulic actuator described above is substantiallydouble the cross-sectional area of the piston rod of the hydraulicactuator, when considered on a radial basis. Such an arrangementprovides the same output force from the hydraulic actuator in eitherdirection, using the same fluid pressure.

In the preferred arrangement described above, a hydraulic actuator isprovided for both the front of the vehicle and the rear of the vehicle,and these hydraulic actuators are substantially the same. In analternative arrangement, the hydraulic actuator for the front of thevehicle may be a different type to the hydraulic actuator for the rearof the vehicle.

In any of the roll control systems described above, the hydraulicactuator may include a check valve (not shown, but preferably mounted inthe piston) which allows flow of hydraulic fluid from the first fluidchamber to the second fluid chamber only when the fluid pressure in thefirst fluid chamber is greater than the fluid pressure in the secondfluid chamber. With such an arrangement, the second fluid chamber can beconnected to a reservoir during servicing of the actuator to bleed airfrom the hydraulic fluid. Also, the presence of the check valve reducesthe risk of air being sucked into the second fluid chamber should thefluid pressure in the second fluid chamber fall below the fluid pressurein the first fluid chamber, and provides further improvements in ridecomfort.

1. A vehicle roll control system for a vehicle having a pair of frontwheels and a pair of rear wheels each rotatable on an axle, comprising:a front torsion bar; a front first arm attached to the front torsion barat one end of the front first arm and being connectable to one of theaxles of the front wheels at the other end of the front first arm; afront hydraulic actuator attached to the front torsion bar; a reartorsion bar; a rear first arm attached to the rear torsion bar at oneend of the rear first arm and being connectable to one of the axles ofthe rear wheels at the other end of the rear first arm; a rear hydraulicactuator attached to the rear torsion bar; and control means connectedto the front and rear hydraulic actuators and controlling the operationthereof on detection of a predetermined vehicle condition; wherein eachfront and rear hydraulic actuator comprises a housing, a piston making asealing sliding fit inside the housing to define a first fluid chamberand a second fluid chamber, and a piston rod connected to the piston andextending through the second fluid chamber and out of the housing;wherein the control means acts on detection of the predetermined vehiclecondition to apply a fluid pressure to the first fluid chamber of thefront hydraulic actuator which is different from a fluid pressureapplied to the first fluid chamber of the rear hydraulic actuator and/orapply a fluid pressure to the second fluid chamber of the fronthydraulic actuator which is different from a fluid pressure applied tothe second fluid chamber of the rear hydraulic actuator; wherein thecontrol means comprises a source of fluid pressure, a fluid reservoir, apressure control valve fluidly connected between the pressure source andthe reservoir, a directional valve fluidly connected between thepressure control valve and the hydraulic actuators, and a pressurerelief valve fluidly connecting the directional valve to the pressuresource or the reservoir; wherein the pressure relief valve is actuatedto create the pressure differential between the first fluid chambersand/or to create the pressure differential between the second fluidchambers.
 2. A vehicle roll control system as claimed in claim 1,wherein the second fluid chambers of the front and rear hydraulicactuators are fluidly connectable to the fluid pressure source, and thefirst fluid chambers are separately fluidly connectable to the fluidpressure source or the fluid reservoir.
 3. A vehicle roll control systemas claimed in claim 2, wherein the control means comprises the pressurerelief valve for fluidly connecting the first fluid chamber of the frontactuator to the pressure source or the reservoir; and a second pressurerelief valve for fluidly connecting the first fluid chamber of the rearactuator to the pressure source or the reservoir.
 4. A vehicle rollcontrol system as claimed in claim 1, wherein the second fluid chamberof the front hydraulic actuator is fluidly connectable to the fluidpressure source; and the first fluid chamber of the front hydraulicactuator and the first and second fluid chambers of the rear hydraulicactuator are separately fluidly connectable to the fluid pressure sourceor the fluid reservoir.
 5. A vehicle roll control system as claimed inclaim 4, wherein the control means comprises: a second directional valvefor fluidly connecting the first fluid chambers of the front and rearactuators to the pressure source or the reservoir; the pressure reliefvalve for fluidly connecting the second fluid chamber of the rearactuator to the fluid source or the reservoir; wherein the seconddirectional valve is positioned in fluid series between the firstdirectional valve and the pressure relief valve.
 6. A vehicle rollcontrol system as claimed in claim 1, wherein the directional valveincludes a first directional valve, in a de-actuated state, fluidlyconnecting the first fluid chambers to one another, and fluid connectsthe second fluid chambers to one another in isolation of the first fluidchambers.
 7. A vehicle roll control system as claimed in claim 1,wherein the directional valve includes a first directional valve, in ade-actuated state, fluidly isolating the first fluid chambers from oneanother, and fluid isolates the second fluid chambers from one anotherand from the first fluid chambers.
 8. A vehicle roll control system asclaimed in claim 1, wherein the directional valve includes a firstdirectional valve, in a de-actuated state, fluidly connecting thepressure source to the reservoir.
 9. A vehicle roll control system asclaimed claim 1, wherein the directional valve includes a firstdirectional valve, in a de-actuated state, fluidly isolating thepressure source from the reservoir.
 10. A vehicle roll control system asclaimed in claim 1, wherein the directional valve includes a firstdirectional valve actuated by a solenoid.
 11. A vehicle roll controlsystem as claimed in claim 1, wherein the directional valve includes afirst directional valve hydraulically actuated by a pilot valve.
 12. Avehicle roll control system as claimed in claim 1, wherein thedirectional valve includes a first directional valve and a seconddirectional valve and the control means further comprises an electroniccontrol module which receives signals dependent on the predeterminedvehicle condition, and which controls the position of the first andsecond directional valves.
 13. A vehicle roll control system as claimedin claim 1, wherein the cross-sectional area of the first fluid chamberof each actuator is substantially double the cross-sectional area of thepiston rod of each actuator.
 14. A vehicle roll control system asclaimed in claim 1, wherein the front hydraulic actuator is attached tothe front torsion bar at one end of the front hydraulic actuator and isconnectable to the other axle of the front wheels at the other end ofthe front hydraulic actuator; and wherein the rear hydraulic actuator isattached to the rear torsion bar at one end of the rear hydraulicactuator and is connectable to the other axle of the rear wheels at theother end of the rear hydraulic actuator.
 15. A vehicle roll controlsystem as claimed in claim 14; further comprising: a second front armrotatably mounted on the front torsion bar at one end of the secondfront arm and being connectable to the other axle of the front wheels atthe other end of the second front arm; wherein the front hydraulicactuator controls the rotation of the second front arm relative to thefront torsion bar; and further comprising a second rear arm rotatablymounted on the rear torsion bar at one end of the second rear arm andbeing connectable to the other axle of the rear wheels at the other endof the second rear arm; wherein the rear hydraulic actuator controls therotation of the second rear arm relative to the rear torsion bar.
 16. Avehicle roll control system as claimed in claim 1, wherein eachhydraulic actuator is attached directly to its associated torsion bar atone end of the hydraulic actuator.
 17. A vehicle roll control system asclaimed in claim 1, wherein each hydraulic actuator is attached to itsassociated torsion bar between axially aligned portions of first andsecond parts of the torsion bar.
 18. A vehicle roll control system asclaimed in claim 1, wherein each hydraulic actuator includes a checkvalve which allows fluid to flow from the first fluid chamber to thesecond fluid chamber when the fluid pressure in the first fluid chamberexceeds the fluid pressure in the second fluid chamber.
 19. A vehicleroll control system as claimed in claim 18, wherein the check valve ismounted in the piston.